When you start at a job for less pay than people in similar positions, correcting the situation can be a challenge.
The pay disparity may have been fair at first. Maybe you went from intern to a job that you had to learn as you did it. In that situation, it’s not unfair to pay you less than an experienced person.
The problem comes when you gain the needed experience and are performing as well as people who make a lot more than you. When that happens, some people find themselves